This would be quite an undertaking, to say the least. To my knowledge, there is no currently maintained open source handwriting recognition layer, so you'd have to write that. Then, you'd need to integrate it deeply into the OS (Possibly into Yunit) and create APIs so apps can take advantage of the handwriting in a new and exciting way.

Humans are remarkably good at making their own custom set of glyphs to mean whatever alphabet they want. I've seen some poor handwriting, and your software would be expected to take that down perfectly.

There have been some handwriting solutions that work letter by letter. You have to draw your characters in their grid. This is not natural. Going further requires a lot of resources, be that time, energy, money, or collected data.

I know it is a difficult thing. But it is not the app who has to read something but are you who has to learn to draw letters in a way the app understands. I see that are many things more important. Thanks.